Modified azo dyestuffs



a'tented Feb. 6v, 17.951

' UNITED STATES v asienta u I MDIFYD #Z0 Y Paul Arthur., Jr.. wiimingien, Dei., assigne; i6 E. I. du -Pont de Nemours & 1Col'ripany", .Wi1' mington, Del., a corporation; ,of Delaware No Drawing. application october go, wie,

' ,SeriaENO-Wzlf -f'riii'e inventien relates te dyeeturfe and mre -partieularly to 'modified azo dyestuis, generally tiff the'pigment dye's'tuff'` class, and to a method ior modifying such clyestuiisv `to produce deepenel shades and reduced bleeding tendencies."

It Well known thatorgar-iic" compounds containing an azo "group have 'been used as 'pigments. lowever, it has been found that an objectionable characteristic of this group, desigvfra-ted as the ato pigment vdyestuis, is that they..

tend :to migrate in organic films "and to dissolve inorganic solvents, Y'tl-nis leading to the phenomenon' :known as bleeding This disadvantage is particularly eyident upon baking overstriped 'films containing the pigments. rlhis characvv higher baking temperatures. Furthermore, the lowcolor strength of simpler aromatic azo compounds precludes their use advantageously 'as pigments. The production off deeper shades, par- 'ticularly inaroons and pur-plesffhas 'heretofore usually necessitated 'the manufacture -of difcultly 'accessible intermediates.

It is an object of this invention to Vprovide =a `process -.for modifying Iazo dye-stuifs to produce 'inore useful fproducts. fA -further yobject is to provide a process 'for-producing 'deepened shades in azo dyestuis, (A, still further object i`s"t'o provide a method lier-reducing the bleeding tendencies shown by azo dyestuiis in organic films. Another jobject-is to yprovide modied azo dyestuis of deepened .shades and hav-ing freduced bleeding vtendencies.V An kadditional 'ob- .ject is to .provide gaa-method .for .eliminating the inhibiting action of the simpler .azodyes .upon

`the setting u-p of drying oils. .Still-another objeet is to 4provide .modified .azo pigments Vof deeper shades,a.such .as vgmaroons Yand puppies.

lOther objects will appear hereinafter.

i These objects :are accomplishedby-thefollow- `.ing invention `Aof modi-fled lazo fdyestuffs .and fa .process tor .preparing them which comprises Jtreating-1in 'the Presence 4of strong sulfuric eacid.:

"as a condensing agent ADI' -2 A azo. dyestui containing at .leastxone :aromatici .nucleus which has at least `one nuclear h ylrogen and .is .substituted Withat least' one azo 'and one hydroxyl group Within .member `olf .the classA 'consisting of 'formaldehyde and .-formaldehyde generators The .reaction lma'ss is subsequent@ drowned in water terminates the. reaction `and .precipitates th V:In the .preferred 'embodiment of this invention, ltheazo dyestui which Vcontains at .least one aro.- Vmatic .nucleus which has ait .least :one Vnuclear hydrogen, yand ione azo and rvone hydroxyl sub- .stitueht is .dissolved or suspended (concentrated sulfuric acid at 1,05 .to 50., SC. .The 'dyestu/.sulfurie acid compfositidn is then brought into. icon- .'tact .with .the formaldehyde #in any'convenient form, .such as paraformaldehyde iin sulfuric `acid solution. It :has also been fou-nd .practicalo Ireversethis Aorder Iof addition.. Any aeid re- 'ssistant vessel .equipped .with an agitator rcan .,b'e

used for carrying outthe reaction. It is vprefierablev to have .seme fume ,control 'attachment :where volatile terms vof A:formaldehyde orlforirialvdehydegen'er'a'tors aresusedf i The reaction .is .allowed 'to 4proceed .for :tl-tree lminutes to .four hours'. vhut preferably'forA not more than. 30 minutes, :and :the reaction 'mass is then drowned vin water.rv Drowning consists :of

xaapidly -.mixing the .acid solution' .with sufficient water so las r,to .stop the reaction, to ldes-troy the solvent power vof the .acid zand .to v.precipitate .the idyes'tuif .in ya lnegstafte of subdivision. lis de- .'.rs'irable :to use avolurne of v.Water at yleast `twice .that ofi Ythe 4:acidic solution; .With .a lia-tieni .17 to :f1-0 volumes fof .Water ;.to 5.1 volume .of soluvtion, .a rise ,in 4temperature of :about v2'0 to BDFEC.

ALamcompanies.the'gdrowningprocess. The product f @iswashed free .ofsaci-d :and .canbe isolated as the ;wet';,pu1;p or can ibedried.toyieldasolid product.

It is desirable that the product ibewash'ed .acid free, particularly .if .fa .dry dyestu Sisto' be obtained. Otherwise .upon removal of water, )the concentration V:of .acid iis increased to' a .point where it tends .Ito martial-ly Aredissolve .the xrely .divided productgand to v:so change-the .'.physicl ...form of .fthe ,:DIQdl-let Lthat it loses itinotorial V.str ehgth.- .Ingadditipn the ipr'e'sence fof laeidrin the Y,pigment has ia Ydeletericms effect ,on :ina'ny pigment-'vehicles The moncf. .felis-l Afand .poly-azo .difesi-iuris containing-. .gat least fone. aromatic nu'cleus .which vhas .at-least one v nuclear ihydr'ogen and is substituted WY :leastl neiazo-and 'o'ne hydroxyl ...groupiareiincl-udcd .vr-ithini-:this invention. ,How-

ever the parent monoand disazo compoundsare preferred because of the greater ease of preparation, greater commercial availability andY lower cost than the more complex polyazo dyestuffs. Some examples of monoazo dyestuffs are 1-(2- nitro-p-tolylazo) -Z-naphthol, 4- (p-nitrophenylazo)resorcinol, and 1-(2-methyl5-ntrophenyl azo) 2 hydroxy 3 naphthanilide. A common disazo dyestuff is 1-[4-(o-tolylazo)-o-tolylazol- Z-naphthol. An example of a polyazo dyestuff is 1 hydroxy 2[3(2,4 dihydroxy phenylazo) phenylazol 6 (2,4 dihydroxy phenylazo) S-naphthalene-sulfonic acid sodium salt.

The pigment dyestuffs-and precipitated azo colors containing a beta-naphthol nucleus in their structure, such as those derived from a 2- hydroxy 3 naphthoic acid, or 2 hydroxy 3 naphtharylides, or beta-naphthol, are particularly susceptible to theI conditions of the process of this invention but are entirely unaffected by the conditions used in after-treating dyed fibers colored with azo dyestuffs derived from resorcinol as described in the prior art. These classes of 4dyestuifs are preferred as reactants in this invention because of their inherentrresistance to deteriorating influences.Y However, the invention is not limited to this preferred group since startling improvement may be made in organic compounds for pigment purposes, particularly in cases such as azoxybenzene which normally are not even considered pigments.v In addition, the so-called oil-soluble colors, such as 1-[4-(0- tolylazo)-o-tolylazol-2-naphthol, are improved through a marked reduction in their bleeding tendency and an elimination of their inhibiting action upon the dryingV of linseed oil vehicles.

The ordinary concentrated sulfuric acid of commerce containing 96% sulfuric acid is quite suitable for use in this invention. Strong sulfuric acid of atleast 80% concentration should 'be used in this invention. Inert diluents may be added to the reaction mixture but in general the addition of polar organic vmaterials tends to inmaterials are themselves the modifying agents.

'Excessive dilution of the sulfuric acid with water or. acetic acid inhibits the reaction.

Itis preferred that the reaction medium. not contain more than 25% polar solvent by weight.

Paraformaldehyde has beenfound to be the Hmost` convenient form of-formaldehyde to use since it is relatively free of odor, easily handled and dissolves in sulfuric acid without heat effects. However the formaldehyde may be added in Iother forms including formalin, formals, methylenediesters, methylol derivatives, and methylol ethers. The addition of the preferred modifying agent, paraformaldehyde, to sulfuric acid results in no readily detectable heat effects whereas the addition of formalin to sulfuric acid produces marked heat effects.

- Modification with formaldehyde according to the process of this invention results in a deepening of the shade of the pigment which is proportional to the amount of formaldehyde or formaldehyde generator added up to approxi- 'mately 1 mole of formaldehyde per mole of pig- 'ment'beyond which further additions of formpigment. However excessive amounts of formaldehyde lshould be avoided since this increases' `hibit the reaction unless these polar organic the bleeding tendency. In general no more'tha'n' 5 moles and preferably not more than 2 moles of formaldehyde per mole of dyestuif should be used. The amount used within these limits will of course depend upon the particular dyestuff being treated. For optimum results about 1.2'

moles of formaldehyde per should be used. e

The temperature should be chosen so that it is high enough to permit ready solution of the mole of dyestuff .dyestuff and to give 'a mobile, easily handled mixture but should not be so high as to cause the sulfuric acid itself to .modify the dyestuff. In practice it has been found that the range of 10 to 50 C., and preferably 15 to 35 C., is ymost convenient and practical for ordinary purposes.y

The reaction occurs with surprising speed and rapidity at normal room temperature so there is no necessity of using extreme temperatures dur- The dyestuff tends to become more bleed resistant as the reaction time is increased provided the necessary minimum amount of formaldehyde generator is present. However, concurrent withy this effect the solution tends to become more viscous and the sulfuric acid itself tends to modify the dyestuff in an undesirable manner. The reaction time can be shortened by decreasing the ratio of dyestuff to formaldehyde, that is by increasing the amount of formaldehyde present. This procedure also tends to .lessen the tendency of the solutions to become more Viscous and gel but on the other hand leads to an excess of unreacted formaldehyde which increases the cost of the process.

Adjuvant agents to prevent gelation of the reaction mixture or to help produce particularly desirable products can be used. Adjuvant agents preferred for use are phenolic-compounds having at least one Z=O type substituent in the same aromatic ring as the hydroxyl group, .where Z represents nitrogen, carbon or sulfur and can be tri, tetra-, Vpenta-, or hexa-valent. yThus. the --Z---OI type substituent includes among others the nitro group, the sulfone group, the ketone group, the ester group, and the nitroso group. Examples of such adjuvant agents are 2-hydroxy-3-naphtho-o-toluide, salicylanilidve, p,p'-dihydroxydiphenylsulfone, p-hydroxybenzophenone, phenyl salicylate, 2,4-dinitrophenol. and p-nitrosophenol. f

This invention is further illustrated by the following examplesin which the quantities are given as parts by Weight unless otherwise specified. Y

Example I Fifty parts (1 mole) of an azo pigment dyestuff, 1- (2,5-dichlorophenylazo`) -Z-hydroxy-B- naphtho-o-toluide, is added to1,4'70 parts of agitated 96% sulfuric acid over a 15-minute period. Avery dark colored solution is formed. The temperature rises approximately 3 C. After 3.5 minutes additional stirring, a solution of 5.33 parts (1.6 moles) of paraformaldehyde dissolved in 69.7 parts of sulfuric acid -is added to the dyestuff solution. The temperature rises approximately 6.7 C. Agitation is continued for 10 minutes and the solution is drowned Vin 6,000 parts of Ywater 11 minutes after the paraformaldehyde addition. The precipitated dyestuff is ing upon mechanical losses during ltration. .portion of the damp. precipitate is dried under fieeietd :br-.vacuum filtration' .and the product 200.'part-portions of water until the. filtrate. is less. than 0.002 normal in acid content'.

The yield. of modied pigment is 50-52 parts. dependf- A vacuum to provide a sample for testing the bleeding tendency, and shade of the pigment.v

-. An ink is prepared by mulling one part of pigment with two partsof varnish drierupon a ground glass plate.v The ink, painted on a tin .plate and overstriped with a white linee-ed oil 'paint showed essentially complete removal of the .bleeding tendency upon being baked at 1 80` V-o'r 24 hours..V A oo ntrolink made from untreated pigment and tested in like fashion bleeds strongly. Theshadexof thel pigmentis deepened ahy; the treatmentfrom a light red'. to. ay light vmaroon color'. y Example II In the ease of certain pigments, most often ythose derived from the arylides of 2-hydroxy-3- naphthoic acid, it has been found that the reac- `tion mix-tureswillgel if allowed to. react for a is' formed. The temperature rises` approximately Y' 1.9 Ci. After 2.5 .minutes additional` stirring, 0.73 .parts (2.2. moles) of paraforrnaldehyde is added to the dyestuff solution. Within -secondsthe temperature rises slightlymore than 6.36 C. and afterithe reaction has beenA stirred. approximately 3. minutes' more, the solution gels. The gel is broken up and stirred into 1,000 parts of' water :RTL5-3 minutes after the formaldehyde addition. v?1?hetw.ater slurry' is. stirred for-'18 minutes and then filtered. Afterf three` wash'ings, each comprising 200parts ofwat'er; the modined pigment reslurriedl in'. 500i parts of. water andI stirred for 3K minutes'. 'Ihisslurry ifs then` filtered and the precipitate washed with 200 part portions of .water until thepH. of. the filtrate reaches 4.75. The. .wett pulpis thenv transferredy to a. vacuum drierV where .thefwater is removed. AY yield of 5.2.7 parts ofmodiiied pigment isobtained.

Upon` being mulled into varnish drier in they ratio of.' 2V parts of vehicle to l part' ofY pigment, an; ink. is. produced which is mountedlon a metal panel in juxtaposition with arcontrolY ink` made from. the. unmodified pigment, and baked for 115 hoursv at- 180911?. The modi-fied pigment shows .nof bleeding throughan overstriped white-linseed Ioil paint even.- after an additional 15l`iour bake at 180" F5, although the control inkmade from the unmodiiiedl pigment bleeds strongly; The color of the modied pigment is light maroon in contrast to they light red color ofthe parent'- azo dyestuif.

i L Example III ,V It has' been possible to; avoid the. gelation de# 'scribed in the previous example,` through the addition of` certainI adjuvants whichr may be typi- 'edlby the ZZ-hydroxy.-S-naphthosortoluide used iii-.the following example-:

` Five parts (1 mole) of anvazopigment'dyestuff, (12.5. -l dichlorophenylazo-" -fi-g.- hydroxy w3 naphtlroioetoluide.. is added` to 147 parts-Otegi@ tated 96% sulfuric acid over a 6.5 minute period, therebyfforming a. dark colored solution. The temperature rises approximately 2.7.o C. The solution is stirred 3.5 minutes and 0.68 part. (2.05 moles) of solid paraformaldehyde is added. The temperature immediately begins to rise and after 30 seconds; a, solution of 6.31 g. of 2'hydroxy3 naphthof-o-toluide dissolved in 92 parts ofconfcentrated sulfuric; acid is added. Withinf'one minute aftery the. addition of the. parafornlalde" hyde the temperature rises 5.3J and ve minutes later reaches, a maximum rise of approximately 6.0" C. In contrast to the. previous example, this solution neither becomes more viscous nor gels even though allowedA to continue4 reacting for 9 minutes, aperiod. three timesv longer than that whichv suiced to cause gelation` of an unmodiiid reaction. The reaction mixture. at the endlof the 9 minute. reaction periodis drowned in 1,000 parts of water. The precipitate isv divided into two parts and each is. washed 6 times with portions of water each of 200 parts. The combined precipitates are then reslurried in 500 parts." of water and stirred for Y1/2' hour; The slurry is filtered and Washed with` four portions of water, each of 100 parts. The wet pulp is transferred to a vacuumdrier Where the water is removed. A yield of. 6.58. parts ofk ai deep maroon modified pigment is obtained. When testedlas in the previous example, the formaldehyde-modiiied pigment showed no detectable bleeding tendency.'-

Fifty parts (l mole) of 'an azo. pigment. dye'- stuff.- 1'(2-methoxy-4z-nitrophenyla2o)L `2Y iy droXy-3-naphtho-o-toluide, is added. to 1,470 parts of agitated concentrated sulfuric acid. A

4solution ofk deep purple color is' formed.` To'v this' I28 minutes. It" is thendrowned in 10,000 parts of distilled water and filtered. The precipitate isreslurried in 6,000 parts of water, stirred for 1/2 hour and refiltered. The modied pigment is transferred t'o-a'n oven maintained jat' 180 F.. .andv the precinctY is` dried to constant weight. Sixty` parts of 'modified pigment' is obtained.

A dried ink made from 2 parts' of. varnish drier andY l part'of vpigment showed no tendency to bleed through an over-stripe of a white linseed oil paint upon being Ibaked for 15 hours. .The modified pigment is deepened in shade from a richl maroon to avery dark purplish maroon'pig.- ment of exceptional covering power.r

1.45 parts (edmoles) of solid?paratormaldehyd'eA is added whereupon the temperature rises 'very rapidly to aboutamaximum: rise of 9.64 AC'. within. 3 minutes. tof stand1-with. occasional; stirring?, .at room'-v teini This reaction=mixture is allowedA temperature rises approximately 2.9c C. After 3.5 minutes additional stirring 0.725 parts (2.2 moles) of solid paraformaldehyde is added and this results in a temperature rise of approximately 8.5 C. within 3 minutes after addition of the paraformaldehyde. The reactionv mixture gels 8 minutes after the addition of paraformaldehyde. The products of both these procedures are non-bleeding, dark purplish-red pigments.

Example VI Pigmente of a precipitated azo class are also modified by treatment with formaldehyde generators in concentrated sulfuric acid solution. As is obvious to one skilled in the-art, provision must be made for replacing the metallic iron which had normally been precipitated by the sulfuric acid solution. Fifty parts (l mole) of a precipitated azo dyestuff, 1- (5-chloro-4-methyl-Z-sulfophenylazo) -2- hydroxy-S-napthoic acid mixed Ca-Ba salt, is added to 1,470 parts of agitated 96% sulfuric acid over a minute period. A deep colored solution f is formed and thev temperature rises approximately 61 C. Agitation is continued for 2 minutes and 4.16 parts (0.95 mole) of paraformaldehyde is added. A temperature rise of approximately 1.1 C. results 'and the reaction mixture is stirred for 38 minutes and is then drowned in 6,000 parts of water. ,y The precipitate is reslurried in 1,000 parts of aqueous sodium chloride solution, refiltered and washed with 4 portions, each of 200 parts, off20% aqueous sodium chloride solution. The modified pigment is then reslurried in 1,000 parts of water and l0 parts of calcium chloride is added to, replace the metallic ion lost upon sulfuric acid treatment. The slurry is filtered and the precipitate washed with 2 pori tions of water, one of 200 parts andthe other of parts. The pulp of modified pigment obtained in this manner shows a` markedly deeper red color than that of the unmodified control. Neither the unmodified control nor the formaldehyde-treated pigment shows a tendency to bleed when tested as in Example I.

Example VII Five vparts (1 mole) of 4-(p-nitrophenylazo)- resorcinol is added to 147 parts of agitated 96% sulfuric acid over a S-minute period. A deep orange-red solution is formed and 0.636 part (1.1 moles) of paraformaldehyde are added. The reaction mixture is drowned in 1,000 parts of water 26 minutes after the formaldehyde addition. The product is isolated by filtration, washing and drying at 180 F.

The color of the modified pigment is a somewhat deeper red than that of the vparent dyestuff but shows special advantages in that it does not inhibit the drying of the ink made with the varnish drier vehicle. In addition, the treated material though showing some bleeding, is very "decidedly more bleed resistant than the parent dyestuff.

Example VIII Compounds having azoxy groupings are rearranged under the reaction conditions to arylazophenols which readily undergo modification upon treatment with formaldehyde generators. This change is accompanied Yby remarkable in'- crease in tinctorial strength as well as bya marked deepening in shade. Y

Five parts (1 mole) of azoxybenzene is added to 147 parts of agitated 96% sulfuric acid over a .B-minute period to form an orange-red solution.

To this is added'0.832 part (1.1 moles) of paraformaldehyde and the whole is allowed to react for 20 minutes. The product is isolated :by drowning the solution in 1,000 parts of water, filtering, washing and drying at 180 F. The treated pigment is dark brown in color and has high tinctorial strength in contrast to the almost transparent azoxybenzene. In addition, the formaldehyde-treated product shows no bleed even though the azoxybenzene before treatment exhibits a slight yellow bleed when tested as in Example I.

Example IX Aqueous formaldehyde solutions may be used as the modifying agent for the pigment dissolved in concentrated sulfuric acid provided that suf.- ficient dilution to inhibit the reaction does not result.

Five parts (1 mole) of an azo pigment dyestuff, 1 (2,5 dichlorophenylazo) 2 hydroxy 3.- naphtlio-o-toluide, is added to 147 parts of agitated 96% sulfuric acid over a 27.5 minute period to yield a very dark colored solution. To this is added 1.436 parts (1.6 moles) of formalin. The heat effect is much greater in this case than when an equivalent amount of solid paraformal.- dehyde is added. The reaction mixturev is drownedin 1,000 parts of water 11 minutes after the addition of the formalin. The product. is isolated by filtration, washing and drying at room temperature in a vacuum drier. By this process a maroon-colored pigment is produced, whichfree from the bleeding tendency exhibited by the light red parent dyestuff when tested as in Ex.- ample I.

It is not necessary to use formaldehyde as such, since formaldehyde generators, that is substances liberating formaldehyde, such as paraformaldehyde and the formals, for example methylal and dioxolane, are capable of modifying the pigment under the reaction conditions specified'herein.

The reduction of bleeding is not a regular function of the amount of formaldehyde added to the reaction mixture. The bleeding tendency of pigments modified with an amount of formaldehyde somewhat less than that which yields a product showing a minimum amount of bleeding exhibit a bleeding tendency very markedly stronger than that of a control or of the preferred modified product.

The addition of water to the concentrated sulfuric acid solvent inhibits the modifying action of the formaldehyde. To obtain optimum results a highly concentrated sulfuric acid solution should be used. Since only small portions l of paraformaldehyde are used in the modification of the pigments, the presence of largeV pro'- portions of polar solvents, such asacetic acid,

. is found to have an inhibiting eect upon the asaltaron` objective of the work is important in determining the exact procedure tov be employed. For instance, it ispossible starting with thev same azo dyestuif,. paraformaldehyde, and sulfuric acid to produce within limits only slight or complete reduction in bleeding tendency, an increase or decrease in the' tinctorial strength, a difficultly or readily lter'able product, Vand a slight or considerable change in shade. The reaction time isv varied according to the object desired of the process in hand. They reaction period must also be determined by choice of conditions so as to obtain the desired objectives Without excessive exposure of the dyestuff to the action of the concentrated sulfuric acid and to avoid the tendency of the acid to solubilize the product in water, thereby causing difficulties in the isolation. In general, the objective has been to producef 'a readily lterable, stable, non-bleeding modified azo dyestuff of reproducible shade.

- The amount of dyestuff which is dissolved depends in large part on the molecular Weight and substituents of theA material. molecular Weight azo dyestuils of the Z-hydroxy- 3-naphthoic acid anilide type, a concentration of 3.5% by weight generally gives mobile solutions which do not increase in viscosity to an excessive degree before the objectives of the reaction are accomplished. The more common lower molecular Weight dyestuffs such as those derived by diazotizing and coupling a substituted aniline with beta-naphthol are more soluble and consequently higher concentrations may be made up without encountering mechanical difficulties. The effect of varying the reaction times and mole ratios of the reactants have been shown in the examples and will guide persons skilled in the art of dyestuff preparation to obtain the particularl objective desired.

To avoid unnecessary complications it is prefrable to use unextended dyestuiis as starting materials. It is common practice in the dyestuffs artto standardize colors with. sodium sulfate orv similar agents and to '-rosinate various lakes.

While theseyadded' agents do not prevent opera-v tion of the process of this invention, they introduce added factors which are best avoided if the unmodified azo dyestuff is available.

Some minor variations in` shade, tinctorial strength andparticle size ofthe modified pigments can be obtained through adjustment of the drowning conditions and methods. High temperature drying of modified pigments contaminated with sulfuric acid is tobe avoided since this normally results in an increase in the' particle size of the color Withia resultant loss in tinctoriialstrength.

The process of modification With formaldehyde, that is' condensation, according to this invention has Vno intrinsic connection With sulfonation.y

lthough normally the conditions of this process do not produce sulfonated products, it has been found that certain specific samples of the pre-V ferred4 class of pigments are particularly'sensitive to the action of sulfuric acid alone.A Such produ-cts simultaneously undergo incidental sulfonation as Well as condensation With formaldehyde in, accordance with the process of this invention.

The modified azo pigments of this invention can be employed in whatever applications the un- With the higher modied azo compounds find Iuse. The products of this invention offer particular advantage inV mese appueanons in that theyare deepened in 1. A process for preparing a modified azo dye-A stuff which comprises dissolving in strong sulfuric' acid of at least 80% concentration, at a temperature of from 10 to 50 C., an azo dyestuf containing at least one azo group which is a sub-- 1 stituent in an aromatic ring having at least onel nuclear hydrogen and at least one hydroxyl group', adding thereto per mole of said azo dyestuff. from. 0.5 to 5 moles of a member selected from the class consisting of formaldehyde and substances generating formaldehyde, and subsequently drowning the reaction mixture in Water'.

2.k A. process for preparing a modiiied azo dye-` 'stuif asset forth in claim 1 in which said sulfuricv acidis in about 96% concentration.

3. A process for preparing a modied azo dyestuff which comprises dissolving in strong sulfuric acid of atleast 80% concentration, at a temperature of from 15 to 35 C., an azo 'dyestuff containing at least one azo group which is a substituent in an aromatic ring having'at least one nuclear hydrogen and at least one hydroxyl group,`

adding thereto per mole of said azo dyestuff from 1" to 2 moles of amember selected from the class:

consisting of formaldehyde and substances generating formaldehyde, andfsubsequently drown.-

ing the reaction mixture in water. y 4. A process for preparingra modified azo dyestuff as set forth in claim 3 in which said sulfuric acid is in about 96% concentration.

stuff which comprises dissolving in strong sulfuric,y acid of at least 80% concentration, at a temperature of from 101 to 50' C., an azo pigment dyestui containing at least one azo group which is a substituent in an aromatic ring having at least one nuclear hydrogen and at least one hydroxyl group, adding thereto per mole of said azo dyestuff from 0.5 to 5 moles of a member selected from the class consisting of formaldehyde and substances generating formaldehyde, and subsequently drowning the' reaction mixture in water.

6. A process for preparing a modified azo dyestuff which comprises dissolving in strong sulfuric acid of at least 80 concentration, at a temperature of from 10 to 50 C., an azo dyestuff con-taining at least one azo group which is a substituent in an aromatic'ring having at least one nuclear hydrogen and at least one hydroxyl group, adding theretoper mole of said azo dyestun from 0.5 to'4 5 moles of paraformaldehyde, and subsequentlydrowning the reaction mixture in Water.

u 7. A`v process for preparing a modified azo dyestun' which comprises dissolving in strong sulfuric acid. of at least-80% concentration, at a temperature: of from 1-0 to 50 C., an azo dyestui contain-v ing at least oneazo group which is a substituent in 'am''aronratic' ring having at least one nuclear lay-'- mixture 'init/water.

5.` A process for preparing a modified azo dye- 11.1. `8. A process for preparing a modified azo dyestuff which comprises dissolving in strong Vsulfuric acid of at least 80% concentration, at a temperature of from 10 to 50 C., an azo dyestuii containing at least one azo group which is a substituent inan aromatic ring having at least one nuclear hydrogen and at least one hydroxyl group, adding. thereto per mole of said azo dyestuffjirom 0.5 to moles of a member selected from the class consisting of formaldehyde and substances generating formaldehyde, vthen adding to the reaction mixture an adjuvant agent consisting of 2-hydroxy-3-naphtho-o-toluide to limit the modification of said azo dyestuff, and subsequently drowning the reaction mixture in water.

9. A process for preparing a modified azo dyestuil which comprises dissolving in strong sulfurie acid of at least 80% concentration, at a temperature of from to 50 C., an azo dyestuff containing a 2-hydroxy-3-naphthoic `acid nucleus, adding thereto per mole of said azo dyestuff from 0.5 to 5 moles of a member selected from the class consisting of formaldehyde and substances generating formaldehyde,Y and subsequently drowning the reaction mixture in sulfuric acid of at least 80% concentration, at ai .temperature of from 10 to 50 C., an azo dyestuff containing a `2naphthol nucleus, adding thereto per mole of said azo-'dyestuff from 0.5 to 5fmcles of a memberl selected from the class consisting of formaldehyde and substances generating formaldehyde, and subsequently drowning the reaction mixture in water.

1 12. A process for preparing a modified azo dyestuiT which comprises dissolving in strong sul-` furicacid of at least 80% concentration, at a temperature of from 10 to 50 C., the azo dyestff 1-(2,5-dichlorophenylazo) 2 hydroxy-3f naphtho-o-toluide, adding thereto per mole of f said azo dyestui from 0.5 to 5 moles of paraformaldehyde, and subsequently drowning the reac-j tion mixture in water.

1132 A modified azo dyestuif obtained bydisf; slvingin strong sulfuric acid of at least 8,0% concentration, at a temperature of from 10j`to' y C., an azo dyestufl containing at leastone azo group which is a substituent in an' aromatic ringhaving at least one nuclear hydrogen and at least one hydroxyl group, adding thereto per Y moleof said azo dyestuff from 0.5 to 5' moles of a" member selected from the class consstinglfof formaldehyde and substances generating' formaldehyde, and subsequently drowning the reaction mixture in water 'thereby precipitating-said modified azo dyestuff. v

El) Y 14. A modified azo pigment dyestuff obtained by dissolving in strong sulfuric acid of at least: concentration, at a temperature of from 10 to 50 C., an azo pigment dyestuf containing at least one azoY group which is a substituent in an aromatic ring having at least one nuclearhydrogen and at least one hydroxyl group, adding;I thereto per mole of said azo dyestuif from 0.5 to: 5 moles of a member selected from the class consisting of formaldehyde and substances generating formaldehyde, and subsequently drowning' the reaction mixture in Water thereby precipitating said modified azo pigment dyestuff. if.'

15. A modified azo dyestuff obtained by dissolving in strongl sulfuric acid of at least 80% concentration, at a temperature of from 10 to 50 C., an azo dyestu'if containing a 2-hydroxy- S-naphthoic acid nucleus, adding thereto perA mole of said azo dyestui from 0.5 to 5 moles of a member selected from the'kclass consisting of formaldehyde and substances generating formaldehyde, and subsequently drowning the reac tion mixture in water thereby precipitating said; modiiied azo dyestuff. l

16. A modified azo dyestuii obtained by dissolving in strong'sulfuricacid of at least 80%" concentration, at a temperature of from 10 to 50 C., an azo dyestuff containing a 2hydroxy 3naphtharylide nucleus, adding lthereto per mole of said azo dyestuf from 0.5 to 5 moles of a member selected from the class consisting of form aldehyde and substances generating formaldehyde, and subsequently drowning the reaction mixturein water thereby precipitating said modified azo dyestuff.

17: A modiiied azo dyestuif obtained'by dis-` solving in strong sulfuric acid of at least 80% concentration, at a temperature of from'lO to 50 C., an azo dyestui containing a Z-naphthol nucleus, adding thereto per mole of` said azo dyestuff from 0.5 to 5 moles of a member selected from .the class consisting of formaldehyde and? substances generating formaldehyde, and sub-I sequently'drowning the reaction mixture in' waterthereby precipitating said modified azo dyestuff.'

PAUL ARTHUR, J R. "f

REFERENCES CITED Ihe following references are of record in thefy ile of this patent:

- UNITED STATES PATENTS 

1. A PROCESS FOR PREPARING A MODIFIED AZO DYESTUFF WHICH COMPRISES DISSOLVING IN STRONG SULFURIC ACID OF AT LEAST 80% CONCENTRATION, AT A TEMPERATURE OF FROM 10* TO 50* C., AN AZO DYESTUFF CONTAINING AT LEAST ONE AZO GROUP WHICH IS A SUBSTITUENT IN AN AROMATIC RING HAVING AT LEAST ONE NUCLEAR HYDROGEN AND AT LEAST ONE HYDROXYL GROUP, ADDING THERETO PER MOLE OF SAID AZO DYE STUFF FROM 0.5 TO 5 MOLES OF A MEMBER SELECTED FROM THE CLASS CONSISTING OF FORMALDEHYDE, AND SUBSESUBSTANCES GENERATING FORMALDEHYDE, AND SUBSEQUENTLY DROWNING THE REACTION MIXTURE IN WATER. 